The present invention relates to a method and to apparatus for capturing digital images of documents. In particular, the invention relates to a method for controlling the capture and processing of the document images.
FIG. 1 illustrates an example of a typical conventional document image scanner 10 of the type using a digital camera 12. The camera 12 is supported above a document 14, and the output from the camera 12 is fed to a computer 16 for display and processing of the captured image. The computer 16 contains an image buffer for storing an input image frame.
FIG. 2 illustrates typical operating modes of the scanner 10. The scanner includes a “live” mode 20 in which a live image is continuously input into the buffer and is displayed on the VDU (Video Display Unit) of the computer 16. The scanner also includes a “frozen” mode 22 in which the image in the buffer is frozen, and the frozen image is displayed. In the frozen mode 22, the image can be processed, for example, to determine the boundaries of text and image areas, and to perform Optical Character Recognition (OCR) on text areas. Generally, it is not practical to process the image in the “live” mode, since the processing operations are computationally slow relative to the incoming image frame rate.
When in use, the operator manually controls the operating mode of the document image scanner 10. The operator selects the “live” mode for viewing the document during positioning (to ensure that the desired document area is within the field of view of the digital camera 12). The operator then switches the scanner to the “frozen” mode, to freeze the image and to process the frozen image.
However, such a scanner necessarily suffers from a delay after the operator has switched to the frozen mode, until the image analysis and processing has been completed. A further disadvantage is that it is unintuitive to the operator to have to manually freeze the image before it can be processed. Moreover, it is inconvenient to have to switch back from the frozen mode to the live mode when a new document is to be positioned in front of the camera. It would therefore be desirable to provide a system that does not suffer from these limitations.